Fate of indigenous bacteriophage in a membrane bioreactor

Indigenous bacteriophage was isolated from a conventional sewage treatment plant treating a largely domestic wastewater. The isolated phage was T-even-like with a mean size of 200 nm and was used to indicate the viral removal efficiency achieved in a bench-scale membrane bioreactor (MBR). The MBR incorporated three flat microfiltration membrane modules which were polyethylene with a pore size of 0.4 μm. When treating settled domestic sewage, the MBR achieved an overall removal rate of phage of 2.3–5.9 log across the treatment process. The membrane alone demonstrated a poor phage removal efficiency, but removal efficiency increased as the filtration resistance was increased. It was proposed therefore, that the biofilm accumulating on the surface of the membrane made a major contribution to phage removal. The MBR demonstrated an almost complete removal of faecal coliforms and faecal streptococci (up to 7 log). By comparison a full-scale treatment plant treating the same settled sewage and incorporating tertiary treatment, achieved only up to 2 log removal of the same excreted phage and bacteria.